The researchers said it also appeared to correct the gene responsible for making a flawed protein that causes APL.

It is possible that arsenic trioxide may be found to be of particular value to patients for whom standard chemotherapy may be unsuitable

Ken Campbell, of the Leukaemia Research Fund

It is not the first time arsenic trioxide has been found to treat leukaemia.

A Chinese study earlier this year found the arsenic used in combination with Atra was an effective treatment.

Lead researcher Dr Ardeshir Ghavamzadeh said: "What this means is that we now have the possibility of offering APL patients a new first-line treatment that avoids conventional chemotherapy.

"It also means that if we have this drug and other effective drugs such as Atra available as well, most patients will be able to avoid the need for bone marrow transplants."

Nerves

But Dr David Grimwade, of Guy's, King's & St. Thomas's School of Medicine, said arsenic trioxide was unlikely to become a first-line treatment in the UK.

He said doctors were still a "little nervous" about possible liver and cardiac complications from using arsenic trioxide.

"Chemotherapy is a very effective form of treatment.

"In western countries, where there is the resources and facilities to put patients through long and intensive course of chemotherapy, I can't see arsenic being used for first-line treatment."

However, he acknowledge it may well be more useful in the treatment of the elderly, who often die earlier in the treatment process.

And he added: "What is interesting about this study is that it directly attacks the underlying causes of the leukaemia, which is particularly relevant in developing countries where there are less resources."

Ken Campbell, clinical information officer at the Leukaemia Research Fund, said it was an "interesting study".

"It is possible that arsenic trioxide may be found to be of particular value to patients for whom standard chemotherapy may be unsuitable."